3 Fundamentals of press design

Blanking processes
flat
punch
U
bevelled
punch
l/2
l/2
lineofengagementofthepunch
Fig. 4.5.10
Blanking force reduction with inclined
punch shape
When calculating blanking energy and blanking forces, in particular
where thin sheet metals are involved, it can happen that a machine is
designed to have adequate energy for blanking but not adequate blanking
force. In these cases, it is possible to reduce the blanking force by
using a bevelled or corrugated punch or a female blanking die.
Example:
Assuming that 100 mm diameter circular disks (cut contour circumference U =
314 mm) are to be produced from 2.5 mm thick sheet steel with a shearing resistance
of k S = 100 N/mm 2 , with the blanking force
2
F = A ⋅ k = 25 . mm ⋅ 314 mm ⋅ 100 N/ mm =
78. 5 kN
S S S
the blanking energy is calculated as follows:
2 2
WS = ⋅FS⋅ s = ⋅ 78500 , N⋅ 00025 . m = 130. 8 N⋅m≈131 Nm
3 3
To ensure the correct location of the blanking die in the press, it is
essential to know the location of the resultant blanking force (frequently
also called the center of blanking forces). At this location, the
sum of the individual forces occurring around the periphery of the
blanking edges is considered to act as a single force. This force should
be applied as far as possible in the center of the slide, as this results in
on-center loading and symmetrical elastic deflection of the press. Oncenter
loading also ensures the best possible die life, and press overload
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
277